The present invention relates to devices for spot-welding of motor-vehicle bodies or subassemblies thereof, of the known type comprising:
a welding station, provided with programmable means for electric spot-welding, PA1 conveyor means, for transporting at least part of the structure to be welded to the station and for transporting the structure after that it has been welded out of the welding station, PA1 at least one pair of locating gates arranged on two opposite sides of the welding station, provided with locating and locking devices for keeping the component elements of the structure to be welded in the proper welding position while welding is being carried out, said gates being displaceable towards and away from each other, between an inoperative mutually spaced apart condition, in which said locating and locking devices are disengaged from the structure to be welded, and a mutually close operative condition, in which said locating and locking devices are able to engage the structure to be welded, PA1 and in which each locating gate is an independent unit, with a base portion movably mounted at the welding station and an upper portion which extends upwardly from the base portion.
A device of the above described type has formed the subject of European patent application EP-A-0 642 878 of the same Assignee. Another device of the same type has also formed the subject of European patent application No. 97830456.6, also of the same Applicant, which has not yet been published at the filing date of the present application.
The Applicant has been producing and marketing a flexible welding system for many years, which is identified under the trademark "ROBOGATE", whose basic concept has been originally disclosed for example in U.S. Pat. No. 4,256,957 and the corresponding German patent No. 28 10 822 and from which a number of subsequent improvements and variants have been originated with the time which have also formed the subject of corresponding patents of the Applicant. The ROBOGATE system has actually determined a turn around in the welding technique of motor-vehicle bodies which was generally used until the end of the seventies and has replaced the previous apparatus used at many car manufacturers throughout the world. In a basic version of this system, it comprises two or more pairs of locating gates which are rapidly interchangeable at the welding station and are adapted to operate on respective types of car bodies, The system is able to operate on bodies also very different from each other, so that a same line can be used for producing different models. A further advantage of the ROBOGATE system lies in that it can be adapted with relatively simple and rapid operations and hence at very reduced costs, to the production of a new body model. Another advantage lies in that a uniform quality of all the models of a same type on which the system operates is assured.
The known technique corresponding to the ROBOGATE system provides that each body to be welded reaches the welding station in a loosely preassembled condition. In fact, upstream of the ROBOGATE welding station there are provided one or more "toy-tabbing" stations, in which the various elements forming the car body are provisionally assembled with each other by bending connecting tabs. This provisional connection is naturally a loose connection, i.e. it allows small displacements of each element with respect to the adjacent element. Just for this reason, the locating gates provided at the welding station are provided with locking devices which engage the various parts of the car body in order to lock them in the proper assembling position before spot welds are carried out by the robots which usually form the welding means provided at the station. Once a number of welding spots sufficient to give a stable geometry to the car body has been carried out (at one or more ROBOGATE stations), the car body proceeds towards further stations for completing welding, which do not require any longer the use of locking devices.